Food web – removing species, invasive species and the energy pyramid

What it shows

A food web shows who eats whom in an ecosystem. Producers such as grass or algae capture light energy by photosynthesis; primary, secondary and tertiary consumers get their energy by eating, and decomposers recycle dead matter into the minerals that producers need. At each step most of the energy is lost through respiration, waste and organisms that are never eaten, so only about a tenth passes upward, which limits food chains to four or five links. Because species are connected, removing one species or adding an invasive predator changes the populations of many others, sometimes far away in the web.

How to use

Choose an Ecosystem, then tap a species to highlight its food chains. Press Remove to take it out and compare the biomass bars with the arrows showing the change since the event. Use Reintroduce to bring it back, Add invasive species to release an alien species, and remove Bacteria, fungi to watch dead matter pile up. Finally, move Energy conversion efficiency between 5 % and 20 % and read the energy pyramid.

Parameters you can change

• Ecosystem Grassland, Freshwater pond
• Energy conversion efficiency 5–20 %
• Event at month 12 None, Remove the top predator, Invasive species arrives, Decomposers lost

Questions to explore

1. If frogs are removed from the grassland, how do grasshoppers, snakes and grass change, and why?
2. Why do food chains in nature rarely have more than four or five links?
3. How can an invasive species with no natural enemies affect the native species?